U.S. patent application number 15/515483 was filed with the patent office on 2018-08-16 for method of making fluoropolymer dispersion.
The applicant listed for this patent is SOLVAY SPECIALTY POLYMERS ITALY S.P.A.. Invention is credited to Valeriy KAPELYUSHKO, Marco MALVASI, Stefana MUSIO.
Application Number | 20180230245 15/515483 |
Document ID | / |
Family ID | 51625968 |
Filed Date | 2018-08-16 |
United States Patent
Application |
20180230245 |
Kind Code |
A1 |
MUSIO; Stefana ; et
al. |
August 16, 2018 |
METHOD OF MAKING FLUOROPOLYMER DISPERSION
Abstract
The invention pertains to a method for making a fluoropolymer
dispersion, said method comprising an aqueous emulsion
polymerization of one or more fluorinated monomers wherein said
aqueous emulsion polymerization is carried out in an aqueous medium
comprising a surfactant mixture [mixture (S)] comprising: at least
one perfluorohexanoic acid or salt thereof [surfactant (C6)], in an
amount of 1 to 5 g/I, with respect to said aqueous medium; and at
least one linear bifunctional perfluoropolyether surfactant
[surfactant (PFPE)] complying with formula (I) here below:
XpOOC--CF.sub.2-0-(CF.sub.20)
.sub.n(CF.sub.2CF.sub.20).sub.m-CF.sub.2--COOXp (I) wherein: Xp,
equal to or different from each other, is a hydrogen atom, a
monovalent metal, preferably an alkaline metal, or an ammonium
group of formula --N(R'.sub.n).sub.4, wherein R'.sub.n, equal or
different at each occurrence, is a hydrogen atom or a
C.sub.1-C.sub.6hydrocarbon group, preferably an alkyl group; n' and
m' are independently integers >0 such that the number average
molecular weight of the surfactant (PFPE) is of 500 to 2500, said
surfactant (PFPE) being used in an amount of 0.005 to 0.5 g/I, with
respect to said aqueous medium.
Inventors: |
MUSIO; Stefana;
(Alessandria, IT) ; MALVASI; Marco; (Novi Ligure,
IT) ; KAPELYUSHKO; Valeriy; (Alessandria,
IT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SOLVAY SPECIALTY POLYMERS ITALY S.P.A. |
Bollate |
|
IT |
|
|
Family ID: |
51625968 |
Appl. No.: |
15/515483 |
Filed: |
September 29, 2015 |
PCT Filed: |
September 29, 2015 |
PCT NO: |
PCT/EP2015/072441 |
371 Date: |
March 29, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C08F 14/26 20130101;
C08L 27/18 20130101; C08F 2/26 20130101; C09D 127/18 20130101; C08K
5/095 20130101; C08L 71/02 20130101; C09D 127/18 20130101; C08K
5/095 20130101; C08L 71/02 20130101; C08L 27/18 20130101; C08K
5/095 20130101; C08L 71/02 20130101 |
International
Class: |
C08F 2/26 20060101
C08F002/26; C08K 5/095 20060101 C08K005/095; C08F 14/26 20060101
C08F014/26; C08L 27/18 20060101 C08L027/18; C08L 71/02 20060101
C08L071/02 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 30, 2014 |
EP |
14187156.6 |
Claims
1. A method for making a fluoropolymer dispersion, said method
comprising an aqueous emulsion polymerization of one or more
fluorinated monomers wherein said aqueous emulsion polymerization
is carried out in an aqueous medium comprising a surfactant mixture
[mixture (S)], wherein mixture (S) comprises: at least one
perfluorohexanoate acid or salt [surfactant (C6)], in an amount of
1 to 5 g/l, with respect to said aqueous medium; and at least one
linear bifunctional perfluoropolyether surfactant [surfactant
(PFPE)] complying with formula (I) here below:
X.sub.pOOC--CF.sub.2--O--(CF.sub.2O).sub.n'(CF.sub.2CF.sub.2O).sub.m'--CF-
.sub.2--COOX.sub.p (I) wherein: X.sub.p, equal to or different from
each other, is a hydrogen atom, a monovalent metal, or an ammonium
group of formula --N(R'.sub.n).sub.4, wherein R'.sub.n, equal or
different at each occurrence, is a hydrogen atom or a
C.sub.1-C.sub.6 hydrocarbon group, preferably an alkyl group; n'
and m' are independently integers >0 such that the number
average molecular weight of the surfactant (PFPE) is of 500 to
2500, said surfactant (PFPE) being used in an amount of 0.005 to
0.5 g/l, with respect to said aqueous medium.
2. The method of claim 1, wherein the mixture (S) comprises at
least one perfluorohexanoic acid salt selected from the group
consisting of sodium salt, potassium salt, ammonium salt.
3. The method of claim 1, wherein the amount of surfactant (C6) is
of at least 1.5 g/l, and/or of at most 5 g/l, with respect to the
aqueous medium.
4. The method of claim 1, wherein the amount of surfactant (PFPE)
is of at least 0.01 g/l and/or of at most 0.25 g/l, with respect to
the aqueous medium.
5. The method of claim 1, wherein the aqueous emulsion
polymerization is carried out at a temperature between 10 to
150.degree. C. and/or at a pressure of between 2 and 50 bar.
6. The method of claim 1, said method comprising the aqueous
emulsion polymerization of tetrafluoroethylene, optionally in
combination with one or more perfluoromonomers selected from the
group consisting of perfluoroolefins having 3 to 8 carbon atoms and
perfluoroalkyl(oxy)vinylethers.
7. The method of claim 1, wherein the amount of solids in the
fluoropolymer dispersion directly resulting from the polymerization
is between 3% by weight and about 40% by weight.
8. The method of claim 1, wherein the particle size (volume average
diameter) of the fluoropolymer is between 40 nm and 400 nm.
9. A fluoropolymer dispersion comprising a surfactant mixture
[mixture (S)], wherein mixture (S) comprises: at least one
perfluorohexanoate acid or salt [surfactant (C6)]; and at least one
one linear bifunctional perfluoropolyether surfactant [surfactant
(PFPE)] complying with formula (I) here below:
X.sub.pOOC--CF.sub.2--O--(CF.sub.2).sub.n'(CF.sub.2CF.sub.2O).sub.m'--CF.-
sub.2--COOX.sub.p (I) wherein: X.sub.p, equal to or different from
each other, is a hydrogen atom, a monovalent metal, or an ammonium
group of formula --N(R'.sub.n).sub.4, wherein R'.sub.n, equal or
different at each occurrence, is a hydrogen atom or a
C.sub.1-C.sub.6 hydrocarbon group, preferably an alkyl group; n'
and m' are independently integers >0 such that the number
average molecular weight of the surfactant (PFPE) is of 500 to
2500.
10. The dispersion of claim 9, wherein the fluoropolymer is
selected from the group consisting of tetrafluoroethylene
homopolymers and tetrafluoroethylene copolymers comprising
recurring units derived from at least one fluorinated
comonomer.
11. The dispersion of claim 9, said dispersion further comprising
at least one non-ionic stabilizing surfactants, generally in an
amount of 1 to 12% by weight based on fluoropolymer solids.
12. The dispersion of claim 9, wherein the monovalent metal is an
alkaline metal, and the C.sub.1-C.sub.6 hydrocarbon group is an
alkyl group.
13. The dispersion of claim 10, wherein the fluoropolymer is a
tetrafluoroethylene copolymer comprising recurring units derived
from hexafluoropopylene, perfluoropropylvinylether,
perfluoromethylvinylether, perfluoroethylvinylether, or mixtures
thereof.
14. The method of claim 1, wherein the monovalent metal is an
alkaline metal, and the C.sub.1-C.sub.6 hydrocarbon group is an
alkyl group.
15. The method of claim 2, wherein mixture (S) comprises the
ammonium salt of perfluorohexanoic acid.
16. The method of claim 3, wherein the amount of surfactant (C6) is
of at least 2 g/l and/or of at most 4.8 g/l, with respect to the
aqueous medium.
17. The method of claim 3, wherein the amount of surfactant (C6) is
of at least 2.5 g/l and/or of at most 4.5 g/l, with respect to the
aqueous medium.
18. The method of claim 4, wherein the amount of surfactant (PFPE)
is of at least 0.02 g/l and/or of at most 0.1 g/l, with respect to
the aqueous medium.
19. The method of claim 5, wherein the aqueous emulsion
polymerization is carried out at a temperature of between
20.degree. C. and 130.degree. C. and/or at a pressure of between 5
and 35 bar.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to European application No.
14187156.6 filed on Sep. 30, 2014, the whole content of this
application being incorporated herein by reference for all
purposes.
TECHNICAL FIELD
[0002] The present invention pertains to a method of making a
fluoropolymer dispersion, and to fluoropolymer dispersion
therefrom.
BACKGROUND ART
[0003] Fluoropolymers, i.e. polymers having a fluorinated backbone,
have been long known and have been used in a variety of
applications because of several desirable properties such as heat
resistance, chemical resistance, weatherability, UV-stability
etc.
[0004] A frequently used method for producing fluoropolymers
involves aqueous emulsion polymerization of one or more fluorinated
monomers generally involving the use of fluorinated surfactants.
Frequently used fluorinated surfactants include perfluorooctanoic
acids and salts thereof, in particular ammonium perfluorooctanoic
acid.
[0005] Recently, perfluoroalkanoic acids having 8 or more carbon
atoms have raised environmental concerns. For instance,
perfluoroalkanoic acids have been found to show bioaccumulation.
Accordingly, efforts are now devoted to phasing out from such
compounds and methods have been developed to manufacture
fluoropolymer products using alternative surfactants having a more
favourable toxicological profile.
[0006] Several approaches have been recently pursued to this aim,
typically involving fluorosurfactants comprising a perfluoroalkyl
chain interrupted by one or more catenary oxygen atoms, said chain
having an ionic carboxylate group at one of its ends, or based on
the use of different dispersants, thus dissociating the nucleating
and stabilizing effect through the use of low molecular weight and
high molecular weight fluorosurfactant, both generally understood
to possess a more environmental friendly profile than C8
perfluoroalkanoic acids.
[0007] Attempts have been hence focused on developing solutions
based notably on shorter chain perfluoroalkanoic acids, inherently
possessing lower bioaccumulation potential.
[0008] Nevertheless, shorter chain perfluoroalkanoic acid
surfactants, like perfluorohexanoate acid surfactants, although
possibly possessing adequate nucleating capabilities, often fail to
possess suitable stabilizing effects so as to sustain high yield
dispersion polymerization of fluoropolymers, in particular of TFE
polymers.
[0009] Mixtures of surfactants have been hence been proposed to
this aim.
[0010] Thus, U.S. Pat. No. 6,395,848 (E.I. DUPONT DE NEMOURS &
CIE) 28 May 2002 discloses a method for the aqueous dispersion
polymerization of fluoromonomers in the presence of a combination
of fluorosurfactants, one of which is a perfluoropolyether
carboxylic acid or sulfonic acid or salt thereof, and the other one
is notably a fluoroalkyl carboxylic acid or salt thereof,
preferably perfluoroalkyl carboxylic acids and salts, having 6-20
carbon atoms, preferably 6-12 carbon atoms.
[0011] The expression "perfluoropolyether carboxylic acid or salt
thereof" is used in said document to encompass any
perfluoropolyether chain structure in which oxygen atoms in the
backbone of the molecule are separated by saturated fluorocarbon
groups having 1-3 carbon atoms and which possesses carboxylic ends.
Among these compounds, perfluoropolyethers with carboxylic ends
(i.e. bifunctional compounds) are disclosed.
[0012] Within this frame, WO 2013/027850 (DAIKIN INDUSTRIES) 28
Feb. 2013 discloses a method for manufacturing an aqueous
polytetrafluoroethylene dispersion, said method including a step of
polymerizing tetrafluoroethylene in an aqueous medium in the
presence of perfluorohexanoic acid or a salt thereof.
[0013] The method disclosed therein possibly include the
simultaneous use of a fluoropolyether acid or salt, having a
molecular weight of 800 to 3500, preferably of 1000 to 2500,
possibly having at one or both end acid group(s), said acid
group(s) being possibly carboxylic acid group(s) phosphonic acid
group(s) or sulfonic acid group(s).
[0014] More particularly, Ex. 3 and Ex. 5 thereof are exemplary
embodiments of polymerization methods wherein tetrafluoroethylene
is polymerized in the presence of a mixture of ammonium
hexafluorohexanoate and of a monofunctional perfluoropolyether with
branched chain of formula --(CF(CF.sub.3)CF.sub.2O)-- of trade name
KRTYOX.RTM. 157 FSL.
[0015] Now, the Applicant has found that while the combination of
ammonium hexafluorohexanoate and said perfluoropolyether, as
disclosed in WO 2013/027850, is effective in achieving a certain
conversion of tetrafluoroethylene, when targeting higher
conversions, this system is ineffective in ensuring acceptable
reaction rates, and high polymer build-up and fouling of reactor,
as well as significant formation of coagulum were observed,
especially when using ammonium hexafluorohexanoate in lower
concentrations.
[0016] The need was hence felt for an improved process for the
aqueous polymerization of fluoromonomers based on the use of
perfluorohexanoate surfactant, but enabling achieving more
advantageous conversions with no reactor fouling or coagulum, hence
providing for improved latex stability in polymerization
conditions, also at reduced concentration of said
perfluorohexanoate surfactant.
DISCLOSURE OF INVENTION
[0017] Thus, in one aspect, the invention relates to a method for
making a fluoropolymer dispersion, said method comprising an
aqueous emulsion polymerization of one or more fluorinated monomers
wherein said aqueous emulsion polymerization is carried out in an
aqueous medium comprising a surfactant mixture [mixture (S)]
comprising:
[0018] at least one perfluorohexanoate acid or salt [surfactant
(C6)], in an amount of 1 to 5 g/l, with respect to said aqueous
medium; and
[0019] at least one one linear bifunctional perfluoropolyether
surfactant [surfactant (PFPE)] complying with formula (I) here
below:
X.sub.pOOC--CF.sub.2--O--(CF.sub.2O).sub.n'(CF.sub.2CF.sub.2O).sub.m--CF-
.sub.2--COOX.sub.p (I)
wherein:
[0020] X.sub.p, equal to or different from each other, is a
hydrogen atom, a monovalent metal, preferably an alkaline metal, or
an ammonium group of formula --N(R'.sub.n).sub.4, wherein R'.sub.n,
equal or different at each occurrence, is a hydrogen atom or a
C.sub.1-C.sub.6 hydrocarbon group, preferably an alkyl group;
[0021] n' and m' are independently integers >0 such that the
number average molecular weight of the surfactant (PFPE) is of 500
to 2500, said surfactant (PFPE) being used in an amount of 0.005 to
0.5 g/l, with respect to said aqueous medium.
[0022] The Applicant has found that when combining the surfactant
(C6) with the surfactant (PFPE) having linear structure and
possessing carboxylic groups at both ends, increased polymerization
rates can be achieved, while maintaining good stability of the
latex, with substantially no build-up and limited coagulum
formation during polymerization.
[0023] The mixture (S) advantageously comprises at least one
perfluorohexanoic acid salt selected from the group consisting of
sodium salt, potassium salt, ammonium salt. Preferably, the
perfluorohexanoic acid surfactant salt is the ammonium salt.
[0024] The amount of surfactant (C6) is generally of at least 1.5
g/l, preferably at least 2 g/l, more preferably at least 2.5 g/l
and/or of at most 5 g/l, preferably at most 4.8 g/l, more
preferably at least 4.5 g/l, with respect to the aqueous
medium.
[0025] The surfactant (PFPE) preferably complies with formula (II)
here below:
X.sub.aOOC--CF.sub.2--O--(CF.sub.2O).sub.a'(CF.sub.2CF.sub.2O).sub.a''---
CF.sub.2--COOX.sub.a (II)
wherein:
[0026] X.sub.a, equal to or different from each other, is a
hydrogen atom or a NH.sub.4 group;
[0027] a' and a'' are integers such that the ratio a''/a' is
comprised between 0.3 and 10, and that the number average molecular
weight is of 500 to 2000, preferably of 600 to 1800.
[0028] The amount of surfactant (PFPE) is generally of at least
0.01 g/l, preferably at least 0.02 g/l and/or of at most 0.25 g/l,
preferably at most 0.1 g/l, with respect to the aqueous medium.
[0029] Best results have been obtained when using a mixture (S)
consisting of from 3 g/l to 4.5 g/l of surfactant (C6) and from
0.02 to 0.06 g/l of surfactant (PFPE), as above detailed, with
respect to the aqueous medium.
[0030] In the process of the invention, one or more fluorinated
monomers, in particular gaseous fluorinated monomers are emulsion
polymerized in said aqueous medium.
[0031] By gaseous fluorinated monomers is meant monomers that are
present as a gas under the polymerization conditions.
[0032] Nevertheless, it may be desirable to add certain monomer to
the polymerization in the form of an aqueous emulsion. For example,
fluorinated monomers and in particular perfluorinated co-monomers
that are liquid under the polymerization conditions may be
advantageously added in the form of an aqueous emulsion. Such
emulsion of such co-monomers is preferably prepared using mixture
(S) as an emulsifier.
[0033] In a particular embodiment, the polymerization of the
fluorinated monomers is started in the presence of the mixture (S),
as above detailed. Additional amounts of fluorinated monomers are
generally added during polymerization.
[0034] The aqueous emulsion polymerization may be carried out at a
temperature between 10 to 150.degree. C., preferably 20.degree. C.
to 130.degree. C. and the pressure is typically between 2 and 50
bar, in particular 5 to 35 bar.
[0035] The reaction temperature may be varied during the
polymerization e.g. for influencing the molecular weight
distribution, i.e., to obtain a broad molecular weight distribution
or to obtain a bimodal or multimodal molecular weight
distribution.
[0036] The pH of the polymerization media may be in the range of pH
2-11, preferably 3-10, most preferably 4-10.
[0037] The aqueous emulsion polymerization is typically initiated
by an initiator including any of the initiators known for
initiating a free radical polymerization of fluorinated monomers.
Suitable initiators include peroxides and azo compounds and redox
based initiators. Specific examples of peroxide initiators include,
hydrogen peroxide, sodium or barium peroxide, diacylperoxides such
as diacetylperoxide, disuccinyl peroxide, dipropionylperoxide,
dibutyrylperoxide, dibenzoylperoxide, di-ter-butyl-peroxide,
benzoylacetylperoxide, diglutaric acid peroxide and
dilaurylperoxide, and further per-acids and salts thereof such as
e.g. ammonium, sodium or potassium salts. Examples of per-acids
include peracetic acid. Esters of the peracid can be used as well
and examples thereof include tert.-butylperoxyacetate and
tert.-butylperoxypivalate. Examples of inorganic initiators include
for example ammonium-alkali- or earth alkali salts of persulfates,
permanganic or manganic acid or manganic acids. A persulfate
initiator, e.g. ammonium persulfate (APS), can be used on its own
or may be used in combination with a reducing agent. Suitable
reducing agents include bisulfites such as for example ammonium
bisulfite or sodium metabisulfite, thiosulfates such as for example
ammonium, potassium or sodium thiosulfate, hydrazines,
azodicarboxylates and azodicarboxyldiamide (ADA). Further reducing
agents that may be used include sodium formaldehyde sulfoxylate
(Rongalite) or fluoroalkyl sulfinates as disclosed in U.S. Pat. No.
5,285,002. The reducing agent typically reduces the half-life time
of the persulfate initiator. Additionally, a metal salt catalyst
such as for example copper, iron or silver salts may be added. The
amount of initiator may be between 0.01% by weight (based on the
fluoropolymer solids to be produced) and 1% by weight. In one
embodiment, the amount of initiator is between 0.05 and 0.5% by
weight. In another embodiment, the amount may be between 0.05 and
0.3% by weight.
[0038] The aqueous emulsion polymerization can be carried out in
the presence of other materials, such as notably buffers and, if
desired, complex-formers or chain-transfer agents.
[0039] Examples of chain transfer agents that can be used include
dimethyl ether, methyl t-butyl ether, alkanes having 1 to 5 carbon
atoms such as ethane, propane and n-pentane, halogenated
hydrocarbons such as CCl.sub.4, CHCl.sub.3 and CH.sub.2Cl.sub.2 and
hydrofluorocarbon compounds such as CH.sub.2F--CF.sub.3 (R134a).
Additionally esters like ethylacetate, malonic esters can be
effective as chain transfer agent in the process of the
invention.
[0040] Examples of fluorinated monomers that may be polymerized in
the process of the invention include partially or fully fluorinated
gaseous monomers including fluorinated olefins such as
tetrafluoroethylene (TFE), chlorotrifluoroethylene (CTFE),
hexafluoropropylene (HFP), vinyl fluoride (VF), vinylidene fluoride
(VDF), partially or fully fluorinated allyl ethers and partially or
fully fluorinated alkyl or alkoxy-vinyl ethers.
[0041] The polymerization may further involve non-fluorinated
monomers such as ethylene and propylene.
[0042] Further examples of fluorinated monomer that may be used in
the aqueous emulsion polymerization according to the invention
include those corresponding to the formula:
CF.sub.2.dbd.CF--O--R.sub.f wherein R.sub.f represents a
perfluorinated aliphatic group that may contain one or more oxygen
atoms.
[0043] Still further, the polymerization may involve comonomers
that have a functional group such as for example a group capable of
participating in a peroxide cure reaction. Such functional groups
include halogens such as Br or I as well as nitrile groups.
[0044] The aqueous emulsion polymerization may be used to produce a
variety of fluoropolymers including perfluoropolymers, which have a
fully fluorinated backbone, as well as partially fluorinated
fluoropolymers. Also the aqueous emulsion polymerization may result
in melt-processable fluoropolymers as well as those that are not
melt-processable such as for example polytetrafluoroethylene and
so-called modified polytetrafluoroethylene. The polymerization
process can further yield fluoropolymers that can be cured to make
fluoroelastomers as well as fluorothermoplasts.
[0045] Fluorothermoplasts are generally fluoropolymers that have a
distinct and well noticeable melting point, typically in the range
of 60 to 320.degree. C. or between 100 and 320.degree. C. They thus
have a substantial crystalline phase. Fluoropolymers that are used
for making fluoroelastomers typically are amorphous and/or have a
negligible amount of crystallinity such that no or hardly any
melting point is discernable for these fluoropolymers.
[0046] The method of the present invention is particularly adapted
for the manufacture of not melt-processable fluoropolymers, and
more particularly for the manufacture of polytetrafluoroethylene
and so-called modified polytetrafluoroethylene.
[0047] According to this embodiment the method of the invention
comprises the aqueous emulsion polymerization of
tetrafluoroethylene, possibly in combination with one or more
perfluoromonomers selected from the group consisting of
perfluoroolefins having 3 to 8 carbon atoms and
perfluoroalkyl(oxy)vinylethers.
[0048] The aqueous emulsion polymerization process of the invention
results in a dispersion of the fluoropolymer in water comprising
the surfactants mixture (S). Generally the amount of solids of the
fluoropolymer in the dispersion directly resulting from the
polymerization will vary between 3% by weight and about 40% by
weight depending on the polymerization conditions. A typical range
is between 5 and 30% by weight, for example between 10 and 25% by
weight.
[0049] The particle size (volume average diameter) of the
fluoropolymer is typically between 40 nm and 400 nm with a typical
particle size between 60 nm and about 350 nm being preferred.
[0050] The fluoropolymer may be isolated from the dispersion by
coagulation if a polymer in solid form is desired. Also, depending
on the requirements of the application in which the fluoropolymer
is to be used, the fluoropolymer may be post-fluorinated so as to
convert any thermally unstable end groups into stable CF.sub.3--
end groups.
[0051] For coating applications, an aqueous dispersion of the
fluoropolymer is desired and hence the fluoropolymer will not need
to be separated or coagulated from the dispersion. To obtain a
fluoropolymer dispersion suitable for use in coating applications
such as for example in the impregnation of fabrics or in the
coating of metal substrates to make for example cookware, it will
generally be desired to add further stabilizing surfactants and/or
to further increase the fluoropolymer solids. For example,
non-ionic stabilizing surfactants may be added to the fluoropolymer
dispersion. Typically these will be added thereto in an amount of 1
to 12% by weight based on fluoropolymer solids. Examples of
non-ionic surfactants that may be added include
R.sup.1--O--[CH.sub.2CH.sub.2O].sub.n--[R.sup.2O].sub.m--R.sup.3
(NS) wherein R.sup.1 represents an aromatic or aliphatic
hydrocarbon group having from 6 to 18 carbon atoms, R.sup.2
represents an alkylene having 3 carbon atoms, R.sup.3 represents
hydrogen or a C.sub.1-3 alkyl group, n has a value of 0 to 40, m
has a value of 0 to 40 and the sum of n+m being at least 2. It will
be understood that in the above formula (NS), the units indexed by
n and m may appear as blocks or they may be present in an
alternating or random configuration. Examples of non-ionic
surfactants according to formula (VI) above include alkylphenol oxy
ethylates such as ethoxylated p-isooctylphenol commercially
available under the brand name TRITON.TM. such as for example
TRITON.TM. X 100 wherein the number of ethoxy units is about 10 or
TRITON.TM. X 114 wherein the number of ethoxy units is about 7 to
8. Still further examples include those in which R.sup.1 in the
above formula (NS) represents an alkyl group of 4 to 20 carbon
atoms, m is 0 and R.sup.3 is hydrogen. An example thereof includes
isotridecanol ethoxylated with about 8 ethoxy groups and which is
commercially available as GENAPOL.RTM. X080 from Clariant GmbH.
Non-ionic surfactants according to formula (NS) in which the
hydrophilic part comprises a block-copolymer of ethoxy groups and
propoxy groups may be used as well. Such non-ionic surfactants are
commercially available from Clariant GmbH under the trade
designation GENAPOL.RTM. PF 40 and GENAPOL.RTM. PF 80.
[0052] The amount of fluoropolymer solids in the dispersion may be
upconcentrated as needed or desired to an amount between 30 and 70%
by weight. Any of the known upconcentration techniques may be used
including ultrafiltration and thermal upconcentration.
[0053] Still an object of the invention are fluoropolymer
dispersions comprising the surfactants mixture (S), as above
described.
[0054] Said fluoropolymer dispersions are typically obtained by the
process of the invention.
[0055] Preferred dispersions are those wherein the fluoropolymer is
selected from the group consisting of tetrafluoroethylene
homopolymers and tetrafluoroethylene copolymers comprising
recurring units derived from at least one fluorinated comonomer,
typically selected from hexafluoropopylene and
perfluoroalkyl(oxy)vinylethers, e.g. perfluoropropylvinylether,
perfluoromethylvinylether, or perfluoroethylvinylether.
[0056] Concentration of surfactants of the mixture (S) in the
fluoropolymer dispersions of the invention can be reduced, if
necessary, following traditional techniques. Mention can be made of
ultrafiltration combined with percolate recycle, as described in
U.S. Pat. No. 4,369,266 (HOECHST AG) 18 Jan. 1983, treatment with
ion exchange resins in the presence of a non-ionic surfactant (as
described in EP 1155055 A (DYNEON GMBH) 21 Nov. 2001), of an
anionic surfactant (as exemplified in EP 1676868 A (SOLVAY SOLEXIS
SPA) 5 Jul. 2006) or of a polyelectrolyte (as taught in EP 1676867
A (SOLVAY SOLEXIS SPA) 5 Jul. 2006).
[0057] Should the disclosure of any patents, patent applications,
and publications which are incorporated herein by reference
conflict with the description of the present application to the
extent that it may render a term unclear, the present description
shall take precedence.
[0058] The invention will now be described in more detail with
reference to the following examples, whose purpose is merely
illustrative and not intended to limit the scope of the
invention.
EXAMPLES
[0059] Raw materials:
[0060] Perfluorohexanoic acid ammonium salt, commercially available
as BAOFLON 6A from Shanghai Shenglei (C6 surfactant, herein below)
was used as received.
[0061] Krytox.RTM. 157 FSL commercially available from DuPont.TM.
is a monofunctional branched PFPE based on a chain comprising
recurring units derived from hexfluoropropylene oxide combined with
one carboxylic acid end group (Krytox.RTM., herein below).
[0062] A difunctional linear PFPE of formula
HOOC--CF.sub.2--O--(CF.sub.2O).sub.n'(CF.sub.2CF.sub.2O).sub.m'--CF.sub.2-
--COOH, having averaged molecular weight of 1600 (Z-DIAC, herein
after) was used.
Example 1C
C6 Surfactant Alone
[0063] A polymerization reactor with a total volume of 90 l
equipped with an impeller agitator was charged with 52 l deionized
water. The oxygen free reactor was heated up to 69.degree. C. and
the agitation system was set to 48 rpm. The reactor was charged
with 1 kg of paraffin wax, a water solution containing 235 g of C6
surfactant and with TFE to a pressure of 20 barg. The
polymerization was initiated by 130 mg of ammonium peroxodisulfate
(NH.sub.4).sub.2S.sub.2O.sub.8 (APS) and 2600 mg of disuccinic acid
peroxide (DSAP) in water solutions. As the reaction started, the
reaction pressure of 20 barg was maintained by the feeding of TFE
into the gas phase. The reaction temperature was increased until
85.degree. C. with a rate of 0.25.degree. C./min. After the feeding
of 12 kg of TFE the monomer inlet valves were closed and the
stirring stopped. The reactor was depressurized, vented and cooled.
The so obtained polymer dispersion was instable and high amount of
coagulum was detected, totalling about 49% of converted TFE. The
measured polymer in latex was found to be 9.4% w/w whereas the
theoretical polymer in latex should have been 18% w/w. The latex
particle diameter was 280 nm according to the Laser Light
Scattering (LLS) and using DSC analysis the heat of second fusion
was 27.3 J/g.
Examples 2C and 3C
[0064] Same polymerization procedure as above detailed for Example
1 was repeated, except that varying the amount of TFE fed and
converted, and the reaction times. Details are summarized in Table
1.
Examples 4 to 6
C6 Surfactant+ZDiac
[0065] Polymerization procedure similar to Example 1 was repeated
but using instead of the water solution containing C6 surfactant
alone, a water solution including both C6 surfactant and ZDiac, in
concentrations and with the amounts of TFE and reaction times as
described in Table 1.
Examples 7C to 9C
C6 Surfactant+Krytox.RTM.
[0066] Polymerization procedure similar to Example 1 was repeated
but using instead of the water solution containing C6 surfactant
alone, a water solution including both C6 surfactant and
Krytox.RTM., in concentrations and with the amounts of TFE and
reaction times as described in Table 1.
TABLE-US-00001 TABLE 1 Reaction C6 Z-DIAC Krytox TFE time Run (g)
(g/l) (g) (g/l) (g) (g/l) (kg) (min) 1C 4.50 -- -- -- -- 12 90 2C
4.50 -- -- -- -- 11 120 3C 4.50 -- -- -- -- 15 90 4 231.4 4.45 2.6
0.05 -- -- 22.7 70 5 179.4 3.45 2.6 0.05 -- -- 19 85 6 226.2 4.35
1.3 0.025 -- -- 20 79 7C 231.4 4.45 -- -- 2.6 0.05 22.5 85 8C 179.4
3.45 -- -- 2.6 0.05 19 100 9C 226.2 4.35 -- -- 1.3 0.025 20 105
TABLE-US-00002 TABLE 2 Polymer content .DELTA.H 2.sup.nd P* in
latex (% wt) Coagulum APS fusion Run (kg/min) measured theoretical
(% wt) (nm) (J/g) 1C 0.13 9 18 49 280 27.3 2C 0.09 9 17 48 n.d.
n.d. 3C 0.17 10 22 56 296 26.3 4 0.32 30 30 0 187 33.9 5 0.22 20 27
25 183 29.9 6 0.25 22 28 22 213 29.0 7C 0.26 30 30 0 192 33.2 8C
0.19 4 27 86 330 34.4 9C 0.19 16 28 41 199 30.0 P*: average
polymerization rate expressed as ratio among the converted TFE and
overall reaction time.
[0067] Data provided in above table well demonstrate that
perfluorohexanoate surfactant alone is unable to effectively
stabilize fluoropolymers during polymerization, hence leading to a
substantial amount of coagulum and very poor solids content in
latex.
[0068] The addition of a linear difunctional PFPE compound is such
to enable maximizing polymerization rate while avoiding coagulation
and/or build-up on reactor walls at higher concentration of
surfactant (C6). When decreasing the amount of surfactant (C6), the
combination with linear difunctional PFPE is more effective in
minimizing coagulum formation and achieving a stable
dispersion.
* * * * *